Type I interferons (IFN) (IFN-α, IFN-β, IFN-ω, IFN-τ) are a family of structurally related cytokines having antiviral, antitumor and immunomodulatory effects (Hardy et al., Blood. 97:473, 2001; Cutrone and Langer, J. Biol. Chem. 276:17140, 2001). The human IFNα locus includes two subfamilies. The first subfamily consists of 14 non-allelic genes and 4 pseudogenes having at least 80% homology. The second subfamily, αII or omega (ω), contains 5 pseudogenes and 1 functional gene which exhibits 70% homology with the IFNα genes (Weissmann and Weber, Prog. Nucl. Acid Res. Mol. Biol., 33:251-300, 1986). The subtypes of IFNα have different specific activities but they possess the same biological spectrum (Streuli et al. PNAS-USA 78:2848, 1981) and have the same cellular receptor (Agnet M. et al. in “Interferon 5” Ed. I. Gresser p. 1-22, Academic Press, London 1983).
The interferon β (IFNβ) is encoded by a single gene which has approximately 50% homology with the IFNα genes.
Gamma interferon, which is produced by activated lymphocytes, does not possess any homology with the alpha/beta interferons and it does not react with their receptor.
All human type I interferons bind to a cell surface receptor (IFN alpha receptor, IFNAR) consisting of two transmembrane proteins, IFNAR-1 and IFNAR-2. IFNAR-1 is essential for high affinity binding and differential specificity of the IFNAR complex (Cutrone, 2001, supra). While functional differences for each of the type I IFN subtypes have not been identified, it is thought that each may exhibit different interactions with the IFNAR receptor components leading to potentially diverse signaling outcomes (Cook et al. (1996) J. Biol. Chem., 271:13448). In particular, studies utilizing mutant forms of IFNAR-1 and IFNAR-2 suggested that alpha and beta interferons signal differently through the receptor by interacting differentially with respective chains (Lewerenz et al. (1998) J. Mol. Biol. 282:585).
Early functional studies of type I IFNs focused on innate defense against viral infections (Haller et al. (1981) J. Exp. Med. 154:199; Lindenmann et al. (1981) Methods Enzymol. 78:181). More recent studies, however, implicate type I IFNs as potent immunoregulatory cytokines in the adaptive immune response. Specifically, type I IFNs have been shown to facilitate differentiation of naïve T cells along the Th1 pathway (Brinkmann et al. (1993) J. Exp. Med. 178:1655), to enhance antibody production (Finkelman et al. (1991) J. Exp. Med. 174:1179) and to support the functional activity and survival of memory T cells (Santini, et al. (2000) J. Exp. Med. 191:1777; Tough et al. (1996) Science 272:1947).
Recent work by a number of groups suggests that IFN-α may enhance the maturation or activation of dendritic cells (DCs) (Santini, et al. (2000) J. Exp. Med., 191:1777; Luft et al. (1998) J. Immunol., 161:1947; Luft et al. (2002) Int. Immunol. 14:367; Radvanyi et al. (1999) Scand. J. Immunol. 50:499). Furthermore, increased expression of type I interferons has been described in numerous autoimmune diseases (Foulis et al. (1987) Lancet, 2:1423; Hooks et al. (1982) Arthritis Rheum 25:396; Hertzog et al. (1988) Clin. Immunol. Immunopathol. 48:192; Hopkins and Meager (1988) Clin. Exp. Immunol. 73:88; Arvin and Miller (1984) Arthritis Rheum. 27:582). The most studied examples of this are insulin-dependent diabetes mellitus (IDDM) (Foulis (1987) supra) and systemic lupus erythematosus (SLE) (Hooks (1982) supra), which are associated with elevated levels of IFN-α, and rheumatoid arthritis (RA) (Hertzog (1988), Hopkins and Meager (1988), Arvin and Miller (1984), supra) in which IFN-β may play a more significant role.
Moreover, administration of interferon α has been reported to exacerbate underlying disease in patients with psoriasis and multiple sclerosis and to induce an SLE like syndrome in patients without a previous history of autoimmune disease. Interferon α has also been shown to induce glomerulonephritis in normal mice and to accelerate the onset of the spontaneous autoimmune disease of NZB/W mice. Further, IFN-α therapy has been shown in some cases to lead to undesired side effects, including fever and neurological disorders. Hence, there are pathological situations in which inhibition of type I IFN activity may be beneficial to the patient and a need exists for agents effective in inhibiting type I IFN activity.